Course:FNH200/2014w Team16 Bread

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Introduction

Sourdough Bread [1]

Sourdough bread is a form of naturally leavened bread that is universally recognized as a major constituent of the human diet. [2] The first sourdough bread was prepared in Egypt during the second millennium B.C, making the production of sourdough bread one of the oldest biotechnological processes. [3]The production of sourdough is characterized by a complex microbial ecosystem, mainly represented by lactic acid bacteria (LAB) and yeasts, whose fermentation confers the resulting high sensory qualities and palatability of the finishing product.[4] The synergistic metabolic activities of the incorporated microorganisms are responsible for producing an acidification and souring influence on the final character of the bread.[5] Attributable to the microorganisms’ symbiotic relationship, sourdough bread acquires distinctive physical properties, such as non-uniform, dense crumb grains, a study crust and a small volume.[6] The addition of sugar, low temperature and pH effectively decelerate the rate of the microorganisms’ metabolic activity and growth in the mixture.[7]

History

The enigmatic history of sourdough constructs a well-established arc outlining the complex development of human civilization, from the emergence of domestic cultivation and domestication to the present.[3] The ancient food commodities accurately summarize the diverse types of knowledge, from the agricultural practices and technological processes through to cultural heritage.[3] Attributable to sourdoughs’ strong linkage to human subsistence and intimate connection to tradition, the practices of civil society and religion, present human beings’ curiosity intensified, expeditiously raising the amount of data collections concerning the bread’s origins, chemistry and its multifarious roles in ancient society.[3] Following extensive studies on the subject of sourdough’s emergence into society, the oldest leavened and acidified bread dating back to 5000 years was discovered in Switzerland, and the first production and consumption of sourdough was tracked back to the second millennium B.C in Egypt.[3] Consequently, the Egyptian civilization was the first population to discover that the process of conjoining ground cereal and water, followed by time, creates a distinctive product with a characteristic acid taste, aroma and sizable volume. Succeeding intricate research, microscopic observations of yeast demonstrated the involvement of lactic acid bacteria, the foam of beer and previously fermented material during the bread-making process. During 800 B.C, the Greek civilization adopted Egyptian techniques and formulas and began developing sourdough for the sole consumption of wealthy individuals.[3] The developing society incorporated bread into their daily votive offerings and sacrifices to Dionysus and regarded the aliment as a high-powered, curative substance. Throughout the European Middle Ages, sourdough remained as a leavening agent, until the emergence of barm from beer brewing processes and purpose-cultured yeast.[8] As the California Gold Rush dawned, the period of feverish migration of workers to gold deposits, the French introduced sourdough techniques to the North Americans by establishing independent retail bakeries in San Francisco, such as the Boudin Bakery.[8]

Chemistry

The production of lactate during lactic acid fermentaion [9]
The production of ethanol and carbon dioxide during alcohol fermentation [9]

When examining the physical and chemical properties of sourdough, an individual would posthaste discover the atypical, large pockets of air, the characteristic pungent, superior flavour and the brittle exterior. These distinctive features of sourdough are largely attributed to the chemical by-products produced by the starter culture, which consists of flour, water, yeast and lactic acid bacteria.[3] Consequently, the chemical reactions responsible for the production of this food commodity needs to be thoroughly understood to advance this discussion.

Fermentation

Fermentation is an enzymatically controlled anaerobic breakdown of energy-rich compounds which generates energy and produces alcohols, organic acids and gases. [10]The metabolic process chemically breaks down carbohydrates and other complex organic substances to acquire an essential molecular unit of currency, known as adenosine triphosphate (ATP). [11] The cellular respiratory process is initiated as glucose is converted into a 3-carbon molecule called pyruvate, accompanied by a net gain of 2 ATP molecules and 2 NADH molecules.[12] Due to the absence of dissolved oxygen, the metabolic pathway continues in the direction of anaerobic fermentation, as tricarboxylic acid cycle is heavily dependent upon the concentration of oxygen in the surrounding environment.[13] Following the completion of glycolysis, two discrete fermentations are able to eventuate, lactic acid or alcoholic fermentation, depending on the available, circumferential chemical compounds. Lactic acid fermentation involves the displacement of a hydrogen molecule from the compound, NADH to pyruvate, creating lactate in the process. [13] The biochemical mechanism transpires in fungi, bacteria and human muscle cells when strenuous exercise introduces temporary oxygen shortages. An alternative route to regenerate NAH+ is alcoholic fermentation, involving the conversion of pyruvate into CO2 and an ethyl alcohol.[13]

Pathways of Sourdough Formation

Sourdough cultures are very complex biological ecosystems due to their microbial composition and interactions with themselves and the ingredients. [14]The majority of lactic acid bacteria incorporated into sourdough starters belong to the genus Lactobacillus. The Lactobacilli are divided into 3 groups, based on their central carbon metabolism: homo-, (obligatory) hetero- and facultative heterofermentative organisms. [15]The homofermentative bacteria follow glycolysis, where 1 molecule of hexose is converted into 2 molecules of lactate, consuming 2 ADP molecules, generating 2 ATP molecules (Pathway A). [15] Contrastingly, the heterofermentative bacteria utilize 1 molecule of hexose to produce 1 molecule of lactate, ethanol, CO2 and ATP (Pathway B) and heterofermentative bacteria covert hexose to lactate only. [15] In the presence of fructose or citrate, the regeneration of NAD+ occurs, allowing the production of acetate, which leads to additional ATP gain. Contrastingly, the yeasts convert glucose molecules to CO2 and ethanol during the fermentative process. Subsequently, the changing conditions in the mixture significantly contribute to the activation of enzymes present and the adjustment of pH selectively enhances the performance of certain enzymes, such as amylases, proteases, phytases and hemicellulases. [16] Lastly, the enzyme-induced changes and the microbial metabolites introduce the technological and nutritional effects of fermented bread. [16]

Symbiotic Relationships

The microbial ecology of sourdough fermentation is multiplex and varied with identification of more than 50 species of lactic acid bacteria (LAB). [17] Succeeding extractive experiments, the predominant species in the fermentative mixture were observed to be Lactobacillus sanfranciscensis and Candida milleri. The sourdough microflora maintains a stable, symbolic relationship that contributes towards the production of chemical compounds which introduce a distinctive texture and flavour to the finished product. Despite their saccharolytic and fermentative metabolism, both organisms derive benefit from this unique, on-competitive, ecological association. [17] Being a heterofermentative, L. sanfranciscensis produces acetic and lactic acids, ethanol and CO2, dropping the pH to 3.5, which is inhibitory to competing organisms, such as Saccharomyces cerevisiae. Due to C. milleris’ acid tolerance, the yeast species benefits from the absence of competition from acid-sensitive yeasts and successively, releases free amino acids that are required by L. Sanfranciscensis. [17] The predominant fermentable carbohydrate observed in sourdough cultures in maltose. Whereas S. Cerevisiae readily ferments the disaccharide, C. Milleri is incapable of performing fermentative chemical reactions with the nutrient, preventing the organisms’ growth. Contrastingly, L. Sanfranciscensis prefers the disaccharide, and fermented the sugar in a particular manner. [17] The aforementioned bacterium employs the cytoplasmic enzyme maltose phosphorylase to hydrolyze accumulated maltose to yield free glucose and glucose-1-phosphate. The latter is isomerized to glucose-6-phosphate which enters the heterofermentative phosphoketolase pathway while the free glucose molecules are released into the extracellular medium. Subsequently, the excreted monosaccharides are made available for the sourdough yeast, C. Milleri which will produce ethanol, alcohols and CO2 resultantly. [17]

Types of Sourdough

There are four types of sourdough fermentation that are classified according to their preparation procedures and the metabolic activities of the main lactic acid bacteria. [8] Each type of sourdough involves different types of flours and wild yeasts, depending on their various geographic regions.

Type 0 sourdough

Type 0 sourdough is recognized as the most traditional procedure to create fermented bread. [18] The formula instructs the maker to combine flour and water at an appropriate temperature, which will introduce pungency and bubbles to the final product. Homofermentative lactic acid bacteria are largely responsible for the formation of this particular sourdough. [18]

Type I sourdough

Traditionally, Type I sourdoughs are known to be firmer doughs that possess a pH range of 3.8 to 4.51. This type of sourdough is fermented in lower incubation temperatures [8], normally between 20 and 30 degrees Celsius. [3] For this traditional form of sourdough, water and flour are added each day in the interest of maintaining the microorganisms. [3] The lactic acid bacteria and yeast that are naturally found in the air and flour multiply in the mixture.

Type II sourdough

This particular sourdough requires high incubation temperatures (over 30 degrees Celsius), long fermentation times (usually up to 5 days)2 and baker’s yeast from the purpose of leavening the dough. [3] Attributable to the higher fermentation temperatures, the rate of yeast growth is decreased or retarded. However, the mixture is allowed to be chilled and stored for up to a week following fermentation. [3] The micro-flora observed in this sourdough bread has the capability to withstand high temperatures and low pH (3.51). [8] Type II sourdoughs are more fluid that Type I sourdoughs and are often produced in industrial tanks, permitting the precise control of temperature. In pursuance of achieving high microbial stability, various drying techniques and liquid pasteurization are employed.[19]

Type III sourdough

Type III sourdough is a drier mixture than the two previous types of sourdoughs and achieves its more dehydrated state through the application of spray and drum drying. [19] Spray drying is a method known to produce dry powder from liquid substances by subjecting them to hot gas. [19] Alternatively, drum drying is a process that subjects a thin film of product to a metal cylinder that is heated using steam, allowing the water to evaporate. [19]This process allows the intermediate to undergo Maillard reactions that will produce a caramelized product. [3] The mixture incorporates lactic acid bacteria that are able to withstand high heat and low water activity. [8]The aforementioned process often destroys flavouring compounds during the heating process. Such major losses are prevented through the application of pasteurization or freeze drying. [19]During the last stages, the mixture is reconstituted with water and set aside to revitalize selected microorganisms, a process commonly known as the reactivation phase. [8] Lastly, this type of sourdough has a longer storage time than the previous types. [8]

Characteristics

Sourdough bread displaying non-uniform crumbs and a rough and thick crust [20]
White bread dislaying uniform crumbs and a thin and smooth crust [21]

Before the middle of the 20th century, the white pan bread, a product standardized by the U.S Food and Drug Administration, accounted for more than 90% of total wholesale bread production in the United States. [22]Thereafter, the American population’s desire for alternative bread varieties escalated as results of the consumers’ nutritional concerns and growing demands for diverse flavours. [23]This newborn trend introduced wheat, whole wheat, multigrain, high-fibre and sourdough bread. [22]

Internal Characteristics

Upon examination of the physical features of the interior region of sour bread, the non-uniform, dense crumb grains, irregular alveolation and the shiny surface of each alveolus would be initially discovered. [24] Succeeding physical contact, the crumbs would be springy, resilient and the detachment of a small segment would not induce damaged to the overall structure. Additionally the sourdough bread would display elasticity when strained, yet firmness and bulkiness. [25]The chemical explanation for this phenomenon reverts to the longer fermentation period for the starter. Unlike sourdough bread, the production process of white bread involves the employment of baker’s year, leading to the creation of uniform crumb grains and thinner cellular walls. [22] Consequently, the finished product would display softness, compressibility and pliability. [22]

External Characteristics

The exterior physical features of the two breads are eminently dissimilar, readily distinguishing the two separate aliments from each other. The outer appearance of white bread is regularly associated with a sizable volume and a thin and smooth crust, whist sourdough is often regarded as having a reduced volume, and a more consolidated exterior. [22]Attributable to the durable flours employed and the high concentration of fermentable carbohydrates, white bread is capable of expanding in volume at an expeditious rate. Due to the low expansion time and the addition of oils on the surface, the aforementioned bread will developed a relatively thin crust. Alternatively, the production of sourdough requires the mixture to ferment and be exposed to heat for a longer time interval, producing a thicker and sturdier crust. [22]

Flavour and Aromaticity

The production of sourdough consists of a distinct fermentation process affected by a complex micro-flora of yeasts and lactic acid bacteria (LAB). [26]The synergistic metabolic activities of the incorporated microorganisms are responsible for producing an acidification or souring influence on the final character of the bread. [27]The acidic, bitter flavour of sourdough is attributable to its high concentration of acetic and lactic acids produced by these organisms; roughly ten times that of conventional bread. [28]The integration of chemical compounds such as fructose, lipase and citrate will precipitously enhance the number of aromatic compounds produced. The volatility of acetic acids is responsible for its evaporation, creating a pungent smell during consumption. In addition, the mixture’s exposition of high temperatures initiates the Maillard reaction between nitrogenous compounds and reduced sugars, generating a number of volatile chemicals, such as esters, alcohols and aldehydes. [29] Sourdough breads will vary in flavouring compounds, due to the differences in flour composition and the blending of the cereal flours. While the flavour is sourdough bread is dependable on the enzymatic reactions, flour type, bacterial-fungal interactions and the lengthy time interval for fermentation, the flavour of conventional bread is more influenced by the thermal reactions during the baking process, resulting in a sweeter, milder product. [29]

Shelf-Life Stability

Bread staling encompasses a combination of physico-chemical, mechanical and sensorial pathways, which contribute to the reduction of quality of the bread. Initially, the bread undergoes gelatinization, a process of breaking down intermolecular starch bonds for the formation of hydrogen bonds with water during the baking process. [18] Upon removal from the heat source, the bread experiences polymer crystallization and the re-association of gelatinized starch molecules into ordered structure, known as retrogradation or “staling.” [3] After cooling, the aforementioned process is responsible for producing a firm, rigid and de-hydrated product. Regarding microbial degradation, conventional breads require the addition of antimicrobial agents to prevent spoilage, while sourdoughs’ high acidic content is responsible for inhibiting bacterial growth. The atmospheric humidity, ambient temperature, and the handling and storage process all influence the duration of freshness of the sourdough.[30]

Nutrition and Health

The sourdough fermentation process appreciably improves the nutritional quality of the finished product and its influence on the consumer’s health. In addition to improving the sensory qualities of whole grain, fibre-rich or gluten-free products, the aforementioned product also actively retards starch digestibility, leading to lowered serum glucose and insulin responses.[31] Sourdough fermentation produces non-digestible polysaccharides and modifies the accessibility of the grain fibre complex to gut micro biota. [16] Consequently, sourdough is an acceptable alternative for diabetics. In addition, sourdough is capable of modulating levels and bio-accessibility of bioactive compounds and improving mineral bioavailability. The action of enzymes during fermentation also causes hydrolysis and solubilisation of grain macromolecules, such as proteins and cell wall polysaccharides, changing nutrient absorption. Lastly, bioactive compounds, such as pre-biotic oligosaccharides, are formed during sourdough fermentations. [16]

Preparation of the Sourdough

Sourdough Starter [32]

In the beginning, a sourdough starter culture is required to initiate the baking process. A sourdough starter is employed to commence the fermentation reactions with the required micro-flora, by adding water, sugar and flour to the yeast medium. [33]Consequently, the eukaryotic fungus utilizes the carbohydrates supplied by the two former ingredients to produce gases and alcohol, which contribute to the lightness and distinct flavour of the finished product. [34]The starter must be continuously fed and protected from unfavourable environments to lengthen its lifespan. Due to the lengthy amount of time required to create the starter, it is crucial to commence the baking process early. On average, this process will transpire over 5 days, depending on the surrounding conditions. [35]

Ingredients for Starter

  • All-purpose flour (or a mix of all-purpose and whole grain flour)
  • Filtered water

Equipment

  • 2-quart glass or plastic container (not metal)
  • Scale (highly recommended) or measuring cups
  • Mixing spoon
  • Plastic wrap or container lid

Procedure

Feeding the starter and wrapping the mixture with plastic wrap [36]
  1. Make the Initial Starter (Day 1): In the beginning, combine 4 ounces of all-purpose flour and 4 ounces of water into a large container. Stir the mixture vigorously until the batter appears to be smooth, sticky and thick. Scrape down the sides and loosely cover the large container with plastic wrap or a lid. The surrounding environment must be a consistent temperature of 70°F to 75°F. Leave the mixture for 24 hours. [35]
  2. Feed the Starter (Day 2): After 24 hours, the mixture will contain small bubbles, indicating the presence of yeast, as fungi have utilized the carbohydrates and produced CO2. The starter should smell fresh and mildly sweet. Once again, combine 4 ounces of all-purpose flour and 4 ounces of water into the large container and scrape down the sides and loosely cover the large container with plastic wrap or a lid. [35]
  3. Feed the Starter (Day 3): The sourdough starter will be dotted with bubbles and it will be visibly larger in volume. The batter will be thicker and the smell will be sour-like and musty. If there are no bubbles forming, give the yeast in the starter another day to produce the gases. Once again, combine 4 ounces of all-purpose flour and 4 ounces of water into the large container, scrape down the sides and loosely cover the large container with plastic wrap or a lid.[35]
  4. Feed the Starter (Day 4): The sourdough starter will display large bubbles and it will be doubled in volume. Once stirred, the starter will lose its thickness slightly and it will produce a vinegar-like smell. Combine 4 ounces of all-purpose flour and 4 ounces of water into the large container, scrape down the sides and loosely cover the large container with plastic wrap or a lid. [35]
  5. Starter is Ready to Use (Day 5): During the last day, the volume of the starter will increase and it will be webbed with bubbles. To maintain the starter, discard halt and “feed” it 4 ounces of all-purpose flour and 4 ounces of water. Stir vigorously until every ingredient is incorporated in the batter. [35]

Maintaining the Sourdough Starter

Following the creation of the starter culture, it is crucial to regularly “feed” the mixture. Discard half of the starter culture and then incorporate the appropriate amount of flour and water into it. Whisk the mixture until the batter appears to be smooth. [35]Cover the container loosely with plastic wrap or a lid and place it in the refrigerator. [35]

Ingredients for Sourdough Bread

  • 2 cups of all-purpose flour
  • 1 ½ cup of sourdough starter
  • ¾ teaspoon of salt
  • 1 tablespoon of olive oil

Equipment

  • Electric mixer with dough hook
  • Plastic wrap
  • Cutting boar
  • Sharp, serrated knife
  • Mister

Procedure II

  1. Mix: Assemble and combine the starter, flour and salt. Using an electric mixer with the dough hook attachment on, knead the mixture until it no longer sticks to the mixing bowl. Ball up the dough and place it in a lightly oiled bowl, turning the ball of dough so as to coat it in the oil. Cover it with plastic wrap and leave it in a warm place with no draft (air currents) so it can rise.
  2. Fermentation: Leave the dough in a room that does not have contact with stray air currents that might decrease the mixture’s overall temperature. After 1-1.5 hours, the dough should have doubled in size.
  3. Fold:Transfer the dough to a lightly floured surface. Sprinkle it with flour and knead it gently, in order to remove any large air bubbles. Knead it into a small circle or discs and then shape it into a tight ball by bringing the edges of the circle up together. Pinch together the seams. Place the dough onto a well-floured cutting board with the seams down. Cover it with kitchen towels and let it rest until it has doubled in size again.
  4. Bake: Preheat a baking stone on the bottom rack of the oven at 400° F. If a baking stone is not available, lightly dust a heavy baking sheet with cornmeal. With a sharp, serrated knife, cut a large X into the top of the dough. Spray the dough lightly with a mister (a spray bottle which produces a fine mist of water). Transfer the dough to the baking stone or sheet. Bake the dough until it displays a golden brown colour and sounds hollow when tapped on the bottom (about 60 minutes). Note that the sourdough bread should posses a darker, thicker crust than conventional breads. Remove the loaf from the oven and let the finished product cool on a wire rack for at least 30 minutes prior to serving.

Government Regulations

The Department of Justice Canada maintains consolidated statutes and regulations for the government of Canada. Falling under this department is the Food and Drugs Act and Food and Drug Regulations. [37] The Food and Drugs Act is administered by the Health Products and Food Branch of Health Canada where standards of identity and composition and food additives are regulated. [38] There are various categorizations of food, all with their own set of standards set by Food and Drugs Act. Bread, found in section B.13.021 on the Canadian Government Food and Drug Regulations website, is defined as “food made by baking yeast-leavened dough prepared with flour and water and may contain,” with a list of 29 ingredients permitted as ingredients for bread or white bread. [39] Additionally, each food group must comply with labeling guidelines, set by the Canadian Food Inspection Agency (CFIA), if sold commercially. Sourdough bread falls under the CFIA’s category of “Grain and Baker Products.” [38] Under this category, the Food and Drug Regulation Act requires flour and bread products to contain added thiamine, riboflavin, niacin, folic acid and iron at the levels prescribed by regulation, due to the losses of vitamins and minerals in the flour during processing. Additionally, manufacturers have the option of adding vitamin B6, d-pantothenic acid, magnesium and calcium at prescribed levels. The Food and Drug Regulation Act requires that these additional nutrients are claimed in advertising and shown on the nutrition facts table. [38]

Import and Export

Statistics Canada and the US Census Bureau report that Canada’s total export of bread to all countries was at an estimated value of $2,029 million CAD in 2014. [40] This was a notable increase from $1,463 million CAD reported in 2010. Canada’s total import of bread was at an estimated $1,648 million CAD in 2014. In the past century, bread has increased in consumer popularity, as more different types of bread are available. In 1900, only 8% of Canadian housewives purchased these food commodities. [40] Approximately 60 years later, more than 95% of house-makers are reported to regularly purchase bread. This is attributed to the new technological developments that are responsible for extending the “shelf life” of many bakery products. Packaging guidelines have been established by Consumer and Corporate Affairs Canada. [40]

Anti-bread movements

As a nearly universally enjoyed product, bread has faced unceasing criticism and rejection from the public who consider this product unhealthy. Although contextually specific and changing in both reason and level of rejection, bread has been criticized for being unhealthily processed for many decades. Changing understandings of ‘healthy’ often demonize starche, found in bread products, as an unhealthy nutrient that should be avoided to preserve health. Additionally, there is a strong gluten-free movement, as more than 44 million individuals claim to have a gluten-free diet. [41] Gluten-free has been described by consumers as: “a mainstream sensation, embraced by both out of necessity and as a personal choice toward achieving a healthier way to live.” [41]

Preservation

Growth of mould on sourdough bread [42]

Level of Acidity

While the desirable pungent flavor is the most noticeable property of sourdough bread, the employment of sourdough cultures in bread manufacture offers additional crucial advantages. Arguably, the most important benefit of the sourdough fermentation is the production of organic acids that are responsible for lowering the overall pH. [17] The emergence of these acidic chemical compounds results in the enhanced preservation and increased shelf-life of the sourdough bread. [43]Consequently, the incorporation of efficient lactic acid bacteria (LAB) will ensure the absence of spoilage-causing microorganisms. In addition, the bacteria will remove certain toxins and anti-nutritional factors found in the mixture. The ideal ratio of lactic acid bacteria (LAB) is 1001:1, as a higher number of LABs could impede the normal leavening action of the yeasts, preventing the dough to grow. Since the pH is normally found to be lower than 4.6, the mixture is considered an acidic food, signifying the lack of spoilage-causing bacteria. [22] Lastly, the acidic conditions enhance the water-binding capacity of the starch granules, which significantly decreases the rate of staling. [17]

Sugar and Salt

Through the biological process known as osmosis, salts and sugars are capable of reaching chemical equilibrium with the sugar and salt content of the sourdough they are in contact with. [44]The interaction results in a reduction of the water activity (aw), a measure of unbound, free water molecules that are necessary for microbial survival and growth.[44] In addition, salts and sugars are capable of interfering with a microbe’s enzymatic activity and destabilizing the molecular structure of its DNA. Lastly, sugars introduce an indirect form of food preservation by accelerating the accumulation of antimicrobial compounds from the growth of certain organisms, such as the conversion of sugar to organic acids by lactic acid bacteria in sourdough. [44]

Low Temperature

Subjecting sourdough cultures to low temperatures will decelerate the metabolic activities of the microorganisms, halting the progression of fermentation. [45]Once refrigerated conditions are introduced, molecular movement is decreased as solid formation transpires, locking particles into rigid crystalline formations. [46]Consequently, the frequency of enzyme-substrate collisions significantly decrease, declining overall enzymatic activity. [46] Due to the microorganisms’ strong reliance on enzymes in the fermentative pathway, the majority of the chemical reaction will not proceed forward. Due to yeasts’ inability to withstand low temperature for long periods of time, the fungus will lose its fermentative capacity, lowering the volume of the finished product.

Final Exam Question

What environmental factors are responsible for extending the storage life of sourdough bread?

  • i. Low pH
  • ii. Low Temperatures
  • iii. Sugar
  • iv. Salt
  • v. High concentration of oxygen
  1. i and ii
  2. i, ii and iii.
  3. ii, iii and v
  4. i, ii, iii and iv
  5. i, iii, iv and v

Answer

The answer for this question is 4. Through the production of organic acids, the lactic acid bacteria in sourdough prohibit the proliferation of spoilage-causing microorganisms, since majority of them are unable to tolerate low pH. Attributable to sugar and salt’s water-binding capacity, the two prevent microbial growth by disallowing chemical and biological reactions to take place. Low temperatures decelerate the metabolic activities of the microorganisms, halting the progression of fermentation. Since oxygen is an oxidation agent, a high concentration of the element will not lengthen the storage life of sourdough.

References

  1. ↑ Stonehouse, Paul. Digital image. Web.
  2. ↑ Charles, John. The History of Bread. 124 Vol. New York: Media Source, 1999.
  3. ↑ 3.00 3.01 3.02 3.03 3.04 3.05 3.06 3.07 3.08 3.09 3.10 3.11 3.12 Gobbetti, Marco, et al. Handbook on Sourdough Biotechnology. Springer US, 2013. >
  4. ↑ Corsetti, Aldo, and Luca Settanni. "Lactobacilli in Sourdough Fermentation." Food Research International 40.5 (2007): 539-58.
  5. ↑ Saikia, Dharma, and Nandan Sit. "Effect of using Sourdough and Frozen Dough for Preparation of Breads on Quality, Shelf Life and Staling." American Journal of Food Technology 9 (2014): 223-30.
  6. ↑ Lee, Jessica. "Yeast Are People Too: Sourdough Fermentation from the Microbe’s Point of View." Web. 3 Mar. 2015. <http://pangea.stanford.edu/~jalee24/docs/JALee_OxfordSymposium_Yeast Are People Too.pdf>.
  7. ↑ Rahman, Shafiur. Handbook of Food Preservation. 167; 167 Vol. Boca Raton: CRC Press, 2007.
  8. ↑ 8.0 8.1 8.2 8.3 8.4 8.5 8.6 8.7 Wikipedia. Wikimedia Foundation. Web. 1 Mar. 2015. <http://en.wikipedia.org/wiki/Sourdough#History_of_sourdough>
  9. ↑ 9.0 9.1 Fermentation. Digital image. Glycolysis, Krebs Cycle, and Other Energy-Releasing Pathways. Web.
  10. ↑ "Everyday Chemistry - The Fundamentals of Fermentation." Everyday Chemistry - The Fundamentals of Fermentation. Web. 1 Mar. 2015. <http://humantouchofchemistry.com/the-fundamentals-of-fermentation.htm>
  11. ↑ "Cellular Respiration." Cellular Respiration. Web. 1 Mar. 2015. <http://biology.clc.uc.edu/courses/bio104/cellresp.htm>.
  12. ↑ "Cell Respiration: Glycolysis." Cell Respiration: Glycolysis. Web. 1 Mar. 2015. <http://www.phschool.com/science/biology_place/biocoach/cellresp/glycolysis.html>
  13. ↑ 13.0 13.1 13.2 Shmoop Editorial Team. "Fermentation and Anaerobic Respiration - Shmoop Biology." Shmoop.com. Shmoop University, Inc., 11 Nov. 2008. Web. 1 Mar. 2015. <http://www.shmoop.com/cell-respiration/fermentation-anaerobic-respiration.html
  14. ↑ Chavan, Rupesh S., and Shraddha R. Chavan. "Sourdough Technology—A Traditional Way for Wholesome Foods: A Review." Comprehensive Reviews in Food Science and Food Safety 10.3 (2011): 169-82.
  15. ↑ 15.0 15.1 15.2 Vermeulen, Nicoline. Aroma Relevant Metabolic Activities of Lactobacilli during Wheat Sourdough Fermentation. Thesis. Thesis / Dissertation ETD, 2006. N.p.: n.p., n.d. Print
  16. ↑ 16.0 16.1 16.2 16.3 Poutanen, Kaisa, Laura Flander, and Kati Katina. "Sourdough and Cereal Fermentation in a Nutritional Perspective." Food Microbiology 26.7 (2009): 693-9.
  17. ↑ 17.0 17.1 17.2 17.3 17.4 17.5 17.6 Hutkins, Robert W. Microbiology and Technology of Fermented Foods. Ames, Iowa: Blackwell Pub, 2006.
  18. ↑ 18.0 18.1 18.2 24. Hui, Y. H., E. Özgül Evranuz, and CRC Press. Handbook of Plant-Based Fermented Food and Beverage Technology. Boca Raton, FL: CRC Press, 2012. Cite error: Invalid <ref> tag; name "(Hui and Özgül 2012)." defined multiple times with different content
  19. ↑ 19.0 19.1 19.2 19.3 19.4 Salim-ur-Rehman, Alistair Paterson, and John R. Piggott. "Flavour in Sourdough Breads: A Review." Trends in Food Science & Technology 17.10 (2006): 557-66.
  20. ↑ Ryan, Patrick. Sourdough Recipes. Digital image. Food Dishes. Web.
  21. ↑ Bread, What’s Better: Easy or Delicious? Digital image. Bakingdom. Web.
  22. ↑ 22.0 22.1 22.2 22.3 22.4 22.5 22.6 Kulp, Karel, and Klaus J. Lorenz. Handbook of Dough Fermentations. 127; 127. Vol. New York: Marcel Dekker, Inc, 2003.
  23. ↑ Aplevicz, Krischina Singer, Paulo José Ogliari, and Ernani Sebastião Sant'Anna. "Influence of Fermentation Time on Characteristics of Sourdough Bread." Brazilian Journal of Pharmaceutical Sciences 49.2 (2013).
  24. ↑ "Judging Sourdough Bread and Artisan Breads." Judging Sourdough Bread and Artisan Breads. Web. 1 Mar. 2015. <http://sourdough.com/blog/johnd/judging-sourdough-bread-and-artisan-breads>.
  25. ↑ Corsetti, A., et al. "Combined Effect of Sourdough Lactic Acid Bacteria and Additives on Bread Firmness and Staling." Journal of Agricultural and Food Chemistry 48.7 (2000): 3044-51.
  26. ↑ De Vuyst, Luc, and Patricia Neysens. "The Sourdough Microflora: Biodiversity and Metabolic Interactions." Trends in Food Science & Technology 16.1 (2005): 43-56.
  27. ↑ Saikia, Dharma, and Nandan Sit. "Effect of using Sourdough and Frozen Dough for Preparation of Breads on Quality, Shelf Life and Staling." American Journal of Food Technology 9 (2014): 223-30.
  28. ↑ Kelly, Clara. "Fermented Foods 3." Fermented Foods 3. Web. 3 Mar. 2015. <http://fermentedfoods3.blogspot.ca/>.
  29. ↑ 29.0 29.1 Spicher, Gottfried, and Werner Nierle. "Proteolytic activity of sourdough bacteria." Applied microbiology and biotechnology 28.4-5 (1988): 487-492.
  30. ↑ Saikia, Dharma, and Nandan Sit. "Effect of using Sourdough and Frozen Dough for Preparation of Breads on Quality, Shelf Life and Staling." American Journal of Food Technology 9 (2014): 223-30.
  31. ↑ Liljeberg, H. G., C. H. Lönner, and I. M. Björck. "Sourdough Fermentation Or Addition of Organic Acids Or Corresponding Salts to Bread Improves Nutritional Properties of Starch in Healthy Humans." The Journal of nutrition 125.6 (1995): 1503.
  32. ↑ Ryan, Patrick. Sourdough Starter. Digital image. Food Recipes. Web.
  33. ↑ Brandt, Markus J. "Sourdough Products for Convenient use in Baking." Food Microbiology 24.2 (2007): 161-4.
  34. ↑ Packham, Richard. "Sourdough and Sourdough Starters." About Sourdough Starter. Web. 3 Mar. 2015. <http://packham.n4m.org/sourdo.html>
  35. ↑ 35.0 35.1 35.2 35.3 35.4 35.5 35.6 35.7 Christensen, Emma. "How To Make Your Own Sourdough Starter - Cooking Lessons from The Kitchen." Web. 3 Mar. 2015. <http://www.thekitchn.com/how-to-make-your-own-sourdough-starter-cooking-lessons-from-the-kitchn-47337>.
  36. ↑ Hamel, P. J. Creating Your Own Sourdough Starter: The Path to Great Bread. Digital image. Flourish. Web.
  37. ↑ "Food and Drugs Act (R.S.C., 1985, C. F-27)." Legislative Services Branch. Web. 10 Mar. 2015. <http://laws.justice.gc.ca/eng/acts/F-27/page-2.html#h-5>.
  38. ↑ 38.0 38.1 38.2 "Food and Drug Regulations." Justice Law Website. Web. 10 Mar. 2015. <http://laws-lois.justice.gc.ca/eng/regulations/c.r.c.,_c._870/FullText.html>.
  39. ↑ "Food and Drug Regulations (C.R.C., C. 870)." Legislative Services Branch. Web. 10 Mar. 2015. <http://laws.justice.gc.ca/eng/regulations/C.R.C.,_c._870/page-140.html#h-96>.
  40. ↑ 40.0 40.1 40.2 Barratt, Robert F. "Baking Industry." The Canadian Encyclopedia. 2 June 2006. Web. 10 Mar. 2015. <http://www.thecanadianencyclopedia.ca/en/article/baking-industry/>.
  41. ↑ 41.0 41.1 "Gluten-Free Market Trends." The GlutenFree Agency. Web. 10 Mar. 2015. <http://thegluten-freeagency.com/gluten-free-market-trends/>.
  42. ↑ Which Type of Bread Grows Mold the Fastest? Digital image. Ask. Web.
  43. ↑ Organic Acids and Food Preservation. 34 Vol. Portland: Ringgold Inc, 2010.
  44. ↑ 44.0 44.1 44.2 "How Do Salt and Sugar Prevent Microbial Spoilage?" Scientific American Global RSS. Web. 3 Mar. 2015. <http://www.scientificamerican.com/article/how-do-salt-and-sugar-pre/>. Cite error: Invalid <ref> tag; name "(Salt and Sugar 2015)." defined multiple times with different content
  45. ↑ "Fermented and Vegetables. A Global Perspective. Chapter 5." Fermented and Vegetables. A Global Perspective. Chapter 5. Web. 3 Mar. 2015. <http://www.fao.org/docrep/x0560e/x0560e10.htm>.
  46. ↑ 46.0 46.1 "What Are the Effects of Boiling & Freezing on Enzyme Activity? | The Classroom | Synonym." The Classroom. Web. 3 Mar. 2015. <http://classroom.synonym.com/effects-boiling-freezing-enzyme-activity-23207.html>.


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